Color cathode ray tube magnetic pole piece support structure

ABSTRACT

The free ends of pairs of magnetic pole shoes of an internal convergence unit in a color CRT resiliently abut against spacing lugs.

States Patent [1 van Leeuwen [451 Dec. 30, 1975 1 COLOR CATHODE RAY TUBEMAGNETIC POLE PIECE SUPPORT STRUCTURE [75] Inventor: Johannes Aloysiusvan Leeuwen,

Emmasingel, Eindhoven,

Netherlands [73] Assignee: U.S. Philips Corporation, New

York, N.Y.

[22] Filed: May 2, 1974 [21] App]. No.: 466,388

[30] Foreign Application Priority Data May 21, 1973 Netherlands 7307040[52} U.S. Cl 313/417; 313/412 [51] Int. Cl. H01J 29/51; l-lOlJ 29/02[58] Field of Search 313/417,4l2,413,414, 3l3/409,428, 441

[56] References Cited UNITED STATES PATENTS 3,548,249 12/1970 Yoshida eta1 313/411 X 3,728,569 4/1973 Gerritsen 1. 313/412 PrimaryExaminer-Robert Segal Attorney, Agent, or FirmFrank R. Trifari; GeorgeB. Berka 57 ABSTRACT The free ends of pairs of magnetic pole shoes of aninternal convergence unit in a color CRT resiliently abut againstspacing lugs.

3 Claims, 5 Drawing Figures US. Patent Dec. 30, 1975 3,930,180

COLOR CATHODE RAY TUBE MAGNETIC POLE PIECE SUPPORT STRUCTURE Theinvention relates to a cathode-ray tube for displaying colored picturesand comprising in' an evacuated envelope means to generate a number ofelectron beams, a display screen comprising a large number of regionsluminescing in different colors, a color selection electrode having alarge number of apertures, and means to converge the electron beams onthe display screen, which electron beams each are assigned toluminescent regions of one color by means of said color selectionelectrode, said convergence means comprising a cylindrical sleeve towhich are secured a number of pairs of ferromagnetic pole shoesextending radially inwards.

Such a cathode-ray tube is known from the US. Pat. No. 3,643,121. Withthe magnetic field which can be produced between each pair of pole shoesof the internal convergence unit by means of an external convergenceunit which is situated outside the envelope of the tube and cooperateswith the pole shoes, the relevant electron beam can be slightlydeflected in a radial direction. This is carried out in such manner thatthe electron beams intersect each other substantially in one point atthe area of the display screen. The simple construction of the internalconvergence unit known from the said patent specification, however,suffers from the drawback that the distance between the pole shoes ofone pair is not determined sufficiently accurately.

It is the object of the invention to mitigate this drawback and toprovide a construction of the internaliconvergence unit in which thedistance between the pole shoes is fixed in a very simple manner.

According to the invention, a cathode ray tube of the type mentioned inthe first paragraph is characterized in that means are present to fixthe inwardly directed ends of the pole shoes, which means are preferablysuch that the inwardly directed ends of the pole shoes are pressedagainst a support under the influence of the resilience of the poleshoes. Said support is preferably manufactured from one piece andcomprises a central portion which is secured to a base plate of the saidcylindrical sleeve, and a lug which is bent in the axial direction foreach pair of pole shoes.

The invention will be described in greater detail with reference to theaccompanying drawing, of which:

FIG. 1 shows a cathode-ray tube for displaying colored picturesaccording to the invention,

FIG. 2 is an elevation of the internal convergence unit of said tube,

FIG. 3 is an axial cross-sectional view of said internal convergenceunit,

FIG. 4 shows supporting means for the ends of the pole shoes and FIG. 5explains an alternative method of supporting.

The cathode-ray tube shown in FIG. 1 for displaying colored pictures isof the shadow mask type and comprises: an evacuated glass envelope 1, aset of electron guns 2 in triangular arrangement for producing threeelectron beams 3, 4 and 5, a display screen 6 comprising a large numberof phosphor dots luminescing in red, green and blue, respectively, acolor selection electrode 7 having a large number of apertures 8, and aset of deflection coils 9 for scanning the display screen 6 with theelectron beams 3, 4 and 5. The electron beams .3, 4 and 5 are convergedon the display screen 6 by means of an internal convergence unit 10 andan external convergence'unit 'l 1. The internal convergence unit 10comprises a cylindrical sleeve' 12 which is coaxial with the axis 13 ofthe tube.

v FIG. 2 is anelevation of the internal convergence unit 10 viewed fromthe side of the shadow mask 7. The cooperation of the internalconvergence unit 10 with the external convergence unit 1 l is showndiagrammatically with an external magnetic circuit 14 having a coil 15.A current through the coil 15 produces a magnetic field between the poleshoes 16 and 17 which causes a radial displacement of the electron beam5. The electron beam 3 is influenced in the same manner by the fieldbetween the pole shoes 18 and 19 and the electron beam 4 is influencedby the field between the pole shoes 20 and 21. In this manner theelectron beams 3, 4 and 5 can be converged in a point on the displayscreen 6. The pairs of poleshoes are screened relative to each other byferromagnetic partitions 22, 23 and 24. The cylindrical sleeve 12 has abase plate 25 which comprises three apertures for passing the electronbeams 3, 4 and 5.

FIG. 3 is a cross-sectional view for further explanation of theconstruction taken on the plane IIIIII of FIG. 2.

The ends of the pole shoes are kept spaced apart by a support 26 whichis stamped from one piece and which is shown in detail in FIG. 4. Thepole shoes are not secured to the support 26 but are pressed against itas a result of their own resilience. The support 26 comprises a centralportion 27 which is spotwelded to the base plate 25 and three lugs 28,29 and 30 which are bent in an axial direction and have bent ends 31, 32and 33 for keeping the poleshoes spaced apart. The resilience of thepoleshoes may of course also act in the opposite direction as is shownin FIG. 5.

The poleshoes 16, l7, 18, 19, 20 and 21 project through slots in thecylindrical sleeve 12 and have bent ends (for example, 34 for poleshoe21) which are secured to the sleeve 12 by means of spot welds. In theknown construction the distance between the poleshoes of one set wasdetermined entirely by the accuracy with which the end 34 had been bent.In the construction according to the invention the distance isdetermined only by the support 26 which can be punched with greataccuracy. Nevertheless the poleshoes need be welded only to thecylindrical sleeve 12 so that the simplicity of the construction ismaintained.

Although the invention has been explained with reference to a tubehaving three electron guns in triangular arrangement, the invention is,of course, not restricted to such a tube. If, for example, the threeelectron guns are situated with their axes in one flat plane theinvention can also be used in which, for example, only pairs ofpoleshoes are present for the two extreme beams.

What is claimed is:

l. A cathode-ray tube for displaying color pictures comprising anevacuated envelope and, within said envelope, means to generate aplurality of electron beams, a display screen having a pluralityofregions luminescing in different colors, a color selection electrodehaving a plurality of apertures to assign each electron beam toluminescent regions of one color, convergence means including acylindrical'sleeve, a plurality of pairs of ferromagnetic pole shoessecured to said sleeve and extending radially inwards to con- 4 meansincluding a support having a central portion secured to said base plateand a plurality of lugs projecting between the free ends of respectivepairs of pole shoes.

3. A cathode-ray tube as claimed in claim 2 wherein said pole shoesresiliently press against said lugs.

1. A cathode-ray tube for displaying color pictures comprising anevacuated envelope and, within said envelope, means to generate aplurality of electron beams, a display screen having a plurality ofregions luminescing in different colors, a color selection electrodehaving a plurality of apertures to assign each electron beam toluminescent regions of one color, convergence means including acylindrical sleeve, a plurality of pairs of ferromagnetic pole shoessecured to said sleeve and extending radially inwards to converge theelectron beams toward the display screen, means to magnetically screensaid pairs of pole shoes from each other, and spacing means abuttingagainst the free ends of each pair of said pole shoes to fix the spacetherebetween.
 2. A cathode-ray tube as claimed in claim 1 wherein saidsleeve is provided with a base plate, said spacing means including asupport having a central portion secured to said base plate and aplurality of lugs projecting between the free ends of respective pairsof pole shoes.
 3. A cathode-ray tube as claimed in claim 2 wherein saidpole shoes resiliently press against said lugs.